1. Field of the Invention
The present invention is directed to a Fresnel lens device, particularly for use on a vehicle to increase the field of view so as to see closely behind the vehicle when backing.
2. Description of the Prior Art
Most automobiles are equipped with a rear view mirror and one or two side mirrors. Yet, often this is not enough. There is still a sizeable blind spot directly behind the car. Many of the newer passenger cars are designed with the front of the car (the engine hood) slanting downward, thus giving the driver a clearer view of the road immediately ahead. At the same time designers of most of the new cars have made the rear trunk higher and some tend to sweep upward which further increases the said blind spot.
The National Safety Council's 1987 edition of "Accident Facts" reports 47,900 Motor Vehicle Deaths for 1986 of which 0.3% were caused while backing up. For example, when backing out of a garage it is common to get into the car and look into the rear view mirror or turn around and look directly out the rear window and hope there is nothing directly behind the vehicle. Too often there are obstacles; even children. The problem is not new.
The problem, however, has been recognized. The Fresnel lens is known and has been used to address the indicated problem in some circumstances. A Fresnel lens is a series of concentric lenses which when viewed along a line of sight approximately perpendicular with the lens demagnifies, but expands the field of view. A Fresnel lens has been used, for example, on the side window of a truck so that the truck driver can see down along the side of the truck to determine if there is a car. Also, a similar lens has been attached to the back window of a van of a type which has a substantially vertical back and a substantially vertical back window. In that case, the operator again gets an expanded field of view and can see quite close to the back of the vehicle. The problem, however, is that most vehicles have a back window which is spaced forwardly from the rear of the vehicle. A lens, if attached to such back window, would only show the trunk and not space directly behind the vehicle. In addition, the back window is often inclined or curved. Both characteristics cause distortion in a Fresnel lens and may even cause it to look opaque. Thus, the problem of seeing close to the back of a vehicle while driving in reverse is generally unsolved for most vehicles.